Can I have simultaneous access from 2 computers to 1 external HD?

June 25, 2006 3:43 PM

USB/Firewire External Harddrives - how can I get simultaneous access from 2 computers?

I have worked with several external HDs now, they have firewire and USB ports, and I usually plug them into a couple of computers using their different ports. The problem is that I can run the HD off the firewire connection with no problem, but if a USB computer comes on, the firewire shuts off and the other PC gets the access. If the USB PC is accessing the HD and Firewire comes on, USB still retains priority. Is this something that everybody has experienced? Is there a way to change the way this works so that I can have simultaneous connections or so that Firewire gets priority?

posted by crazy finger to computers & internet (16 comments total)

Connect the drive via FireWire, set up file sharing on that workstation (Mac OS X, Windows, Mac OS X to Windows, Windows to Mac OS X). Connect from the other workstation via file sharing.
posted by Blazecock Pileon at 3:53 PM on June 25, 2006

I would do the filesharing, I guess, but it's slower than USB or Firewire b/c we're on a wireless network.

Is there any way at all that this "USB-takes-priority-over-Firewire" policy can be changed?
posted by crazy finger at 3:55 PM on June 25, 2006

Not that I know of, without somehow going into the firmware on the drive controller. I haven't read of it being done, in any case.

You might consider a low-cost FireWire SAN, which you can share among multiple machines, or setting up an entirely 802.11g wireless network to get faster wireless file sharing.
posted by Blazecock Pileon at 4:00 PM on June 25, 2006

Connecting multiple machines simultaneously to a drive enclosure's IO ports is not supported by most drive enclosures - I'm surprised your enclosure works as well as you describe. Connecting the drive to one machine and accessing it via file sharing is probably the best solution. However, you could also connect the drive enclosure via a single USB or firewire cable to either a USB switch or a firewire switch, and then connect your two machines to the switch.
posted by RichardP at 4:13 PM on June 25, 2006

There's no way for this to work. The data format on hard drives is designed with the assumption that only one computer can access it at a time. When you use sharing over a network, really all that's happening is the host computer is accessing the files on the remote computer's behalf.

With the scenario you want, both computers would be able to modify the file system directly. I'm not talking about accessing the same file at once, because the drive (and USB and FireWire) don't know anything about files. They read and write directly form the raw blocks and sectors of the drive. Your disk would become corrupted within seconds of trying this.
posted by cillit bang at 4:28 PM on June 25, 2006

low-cost FireWire SAN

SanCube is ~$3,500 for 1.2TB. Our definitions of "low-cost" differ.

The OP would probably benefit most by sharing out the disk over a network for NAS. If spending small sums of money is okay, getting a box with FW/USB, installing a few disks, and sharing it out is probably also going work.
posted by meehawl at 4:30 PM on June 25, 2006

Our definitions of "low-cost" differ.

Without respect to cost, what the OP wants is something best set up with a SAN, since he wants to connect both machines to the storage with a very fast connection.

Compare the FireWire SAN that to the cost of a Fibre Channel SAN. $3500 is really pocket change.

File sharing is cheap (free) but does not apparently solve the OPs problem.

Consumer-grade wireless products go up to 54 Mbps, which at best is about 7-8 times slower than FireWire, not taking into account overhead from the other hardware and software layers of abstraction introduced by a NAS device.
posted by Blazecock Pileon at 4:40 PM on June 25, 2006

Network attached storage for USB drives.
posted by blue_beetle at 4:49 PM on June 25, 2006

ahem. Network Attached Storage for USB drives.
posted by blue_beetle at 4:50 PM on June 25, 2006

You can, in fact, run a network over firewire on Macs. i don't know if you can on PCs, out of the box. In theory, this gives you 400MB/s networking, faster than an ethernet network. A drive shared over that connection should be nearly as fast as if it was mounted locally. This is a somewhat hidden and under-documented business, though.

There are many networked drives/NAS servers now appearing in the sub-$500 price range. That's no different, really, than file sharing over an ethernet network. But it does cut down on the need for separate drives.
posted by spitbull at 4:52 PM on June 25, 2006

blue_beetle nails a perfectly reasonable option.
posted by spitbull at 4:52 PM on June 25, 2006

By the way, crazy finger, what you are currently doing can cause file corruption and data loss. I believe it can also fry the drive's controller. Not recommended.
posted by spitbull at 4:53 PM on June 25, 2006

what the OP wants is something best set up with a SAN

With respect, I believe SAN is overkill over too expensive for OP and NAS is indicated.

This thread now requires new acronyms.
posted by meehawl at 5:00 PM on June 25, 2006

what about something like this? Network Storage Link?

probabaly not Robust per se, but its cheap. I'm trying to figure out storage i can share between a desktop pc and a macbook.
posted by th3ph17 at 10:06 PM on June 25, 2006

cillit bang has the most important point. Aside from some relatively exotic solutions, the drive has to be (logically) attached to only one computer, or else they'll step on each others' toes and corrupt the filesystem.
posted by hattifattener at 10:48 PM on June 25, 2006

I have the NSLU2 hooked up to a wireless router as the backup volume for the computers on our home network. It works great.
posted by Lazlo at 11:26 AM on June 26, 2006